Aerodynamical profiles having shapes that provide high lift/drag ratios such as laminar profiles are not used on wind turbine blades because they are very sensitive to leading edge roughness.
Wind turbine blades generally have shapes with a sharp trailing edge or a moderately blunt trailing edge, due on some occasions to production deviations, from which the wake is shed. The strength, distribution and direction of wake turbulence separation and vorticity, and the location of the beginning of the wake are sources of increased drag and reduced lift, both of which are highly undesirable.
Trailing edge devices intended to increase lift are known although they usually have a negative effect on drag.
One of these devices is a Gurney flap, shown schematically in FIG. 1, mounted perpendicularly to the chord. A Gurney flap produces two vortices that form a separation bubble that cause a lift increase. It also postpone the separation of the airflow allowing a good behaviour at high angles of attack. However the Gurney flap causes extra drag.
EP 1 314 885 discloses a trailing edge device consisting of a serrated panel to be attached to the trailing edge of the blade.
DE 10021850 discloses a trailing edge extension that can take different geometries by elastic deformation.
None of these devices produces a satisfactory increase of wind turbine efficiency, therefore a continuing need exists for wind turbine blades with an aerodynamic optimised profile.